Molten aluminum resistant refractory composition containing ceramic fibers

ABSTRACT

A ceramic fiber containing refractory moldable composition suitable for use with molten aluminum alloys, the composition comprised of 10-20 wt. % ceramic fiber, 30.5-45 wt. % colloidal silica, 30-45 wt. % total content of liquid carrier, 0.5-5 wt. % organic polymer and 1-25 wt. % barium sulfate. The composition has a high level of resistance to attack or penetration by molten aluminum.

Cross Reference to Related Applications

This application is a continuation-in-part of U.S. Ser. No. 344,689, nowabandoned filed Apr. 28, 1989.

BACKGROUND OF THE INVENTION

This invention relates to refractory compositions, and moreparticularly, it relates to moldable refractory compositions containingceramic fibers having high resistance to molten aluminum alloys.

There are many commercially available refractory products orcompositions which are designed for use with molten aluminumapplications. These products include dense refractory brick, castablesand plastic ramming mixes. Also available are light-weight insulatingcastables. These products contain additives which reduce reactionsbetween the refractories and molten aluminum alloys. For example, LaBarU.S. Pat. No. 4,088,502 discloses a corrosion resistant castablerefractory comprised of calcium aluminate, zinc borosilicate frit andfused silica. Lobaugh U.S. Pat. No. 2,516,892 discloses a refractoryconcrete which uses calcium aluminate cement, a refractory aggregate andan insoluble frit. Hofmann U.S. Pat. No. 4,060,424 discloses a rammingor gunning cement using boric acid and a low temperature softening glassor frit. Talley et al U.S. Pat. No. 4,126,474 discloses aphosphate-bonded alumina or alumino-silicate refractory for liningaluminum-melting furnaces and other containers for molten aluminumincluding 0.5 to 30 wt.% BaSO₄. U.S. Pat. No. 4,174,331 discloses arefractory moldable composition which, upon drying, sets up torefractory shapes which are strongly adherent to the molding surfacesand are essentially crack-free, contains about 45 to about 65% of aliquid vehicle, such as water; about 21 to about 26% ceramic fiber;about 7 to about 30% finely divided silica; and sufficient adhesionenhancing agent to impart from about 18 to about 50 grams per squarecentimeter adherence to steel.

Yet in spite of these disclosures there is still a great need for arefractory composition having improved properties and which has a highlevel of resistance to molten aluminum.

SUMMARY OF THE INVENTION

It is an object of this invention to provide an improved moldablerefractory composition.

It is another object of this invention to provide a moldable refractorycomposition for use in containers for molten aluminum such as used inmelting operations.

It is yet another object of this invention to provide an improvedmoldable refractory composition having improved resistance to moltenmetal attack or penetration.

These and other objects of this invention will be obvious from thedescription and claims.

In accordance with these objects, there is provided a ceramic fibercontaining refractory moldable composition suitable for use with moltenaluminum alloys, the composition comprised of about 10-20 wt.% ceramicfiber, 30.5-45 wt.% colloidal silica, 30-45 wt.% total content of liquidcarrier, 0.5-5 wt.% organic polymer and 1-25 wt.% barium sulfate. Thecomposition has a high level of resistance to attack or penetration bymolten aluminum.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The refractory composition in accordance with the present invention cancontain 10-20 wt.% ceramic fibers, 30.5-45 wt.% colloidal silica, 30-45wt.% liquid carrier, 0.5-5 wt.% organic polymer and 1-25 wt.%,preferably 1-15 wt.%, barium sulfate. Preferably, the compositioncontains 14-18 wt.% ceramic fibers, 35-42 wt.% colloidal silica, 34-42wt.% liquid carrier or vehicle, 0.5-2.5, typically up to 1.8 wt.%organic polymer and 2-10 wt.% barium sulfate, typically 2 to 6 wt.%. Atypical composition is 16 wt.% ceramic fibers, 39 wt.% colloidal silica,39 wt.% liquid carrier, 1 wt.% organic polymer and about 5 wt.% bariumsulfate.

The ceramic fiber can be selected from alumina, aluminum silicate,mullite, calcium aluminum silicate, mineral wool or silicon carbide. Thepreferred type of ceramic fiber is aluminum silicate available from TheCarborundum Company under the name Fiberfrax. Other aluminum silicateswhich can be used are obtained from Johns Manville under the nameCerafiber, or from A.P. Green Refractories under the name Inswool.Fiberfrax is a ceramic fiber made from alumina and silica. The ceramicfiber can contain about 51 wt.% alumina and about 47 wt.% silica and maybe chopped, e.g., from about 1/2 to 1 inch long and about 2 microns indiameter and retains its properties to 1260° C. and under someconditions up to 1648° C.

The colloidal silica used in the invention may contain between 15 and50% solids and have a mean particle size of about 5 to 60 millimicrons.Colloidal silica suitable for use in the invention is available fromNalco Chemical Company and is referred to as Nalcoag 1130, 1140, 1050and 1060.

The liquid vehicle can be water or a combination of water and ethyleneglycol with up to 50 wt.% ethylene glycol. It should be noted that watercan be totally or partially supplied by the liquid fraction of thecolloidal material, e.g. colloidal silica. Other alcohols that may beused include ethanol and diethylene glycol.

The organic polymer is employed as a thickening or adhesion enhancingagent and may be selected from liquid or powder anionic, cationic ornon-ionic high molecular weight organic polymer materials. The polymerscontain polar groups that impart adhesive-type properties. Examples ofsuch are the amide groups, amine groups, ether groups, hydroxyl groupsand carboxyl groups. Particularly useful are theacrylamide/acrylate-derived polymers, such as Nalco 2388 and 7879available from Nalco Chemical Company. Other amide-derived polymers arethe Reten type produced by Hercules, Inc. Other suitable polymers arethe hydroxyl or carboxyl methylcellulose type, such as Methocel,available from Dow Chemical Company. Also suitable are the polyethyleneoxide polymers, such as the Polyox type, available from Union CarbideCorporation.

The polymer, when added in small quantities, acts as a thickening agentand improves the adhesion qualities of the finished product, which aidsin moldability. Other polymers are described in the aforementioned U.S.Pat. No. 4,174,331, incorporated herein by reference. Polymers whichhave been found useful in the present invention are Nalcoag 7879 and2388 available from Nalco Chemical Company.

The barium sulfate useful in the invention can have a purity level of95% or more, with the remainder clay. Such material is available asnatural barytes. This material is available from Cyprus Mining Companyand referred to as #22 Barytes, Barimite-XF and Barimite. If a higherpurity form of barium sulfate is desired, it can be obtained from theCharles A. Wagner Company under the name AMBAR-C. The barium sulfate isnormally provided or ground to a mean particle size of about 10 μm.

These ingredients are blended together to provide a refractorycomposition. For purposes of blending, it is preferred to dissolve thepolymer in the liquid prior to adding the solid materials.

If colloidal alumina is used, the amount is in the range of 5 to 17wt.%, and the liquid level, e.g., water or ethylene glycol, is in therange of 60 to 80 wt.%, preferably 68 to 78 wt.%. The ceramic fiber,organic polymer and barium sulfate are maintained at the same level asfor the silica system.

The colloidal alumina may be about 10 to 20% solids with a mean particlesize of about 2 to 50 millimicrons. An example of this material isNalcoag ISJ-614 manufactured by Nalco Chemical Company.

The following example is further illustrative of the invention.

A molding composition was prepared by pre-blending 23 grams of Nalcoag2388 polymer with 1771 grams of Nalcoag 1050 colloidal silica in aHobart mixer. To this mixture, 362 grams of Fiberfrax 7000 Fiber and 114grams of #22 Barytes barium sulfate were added. The total mixture wasmixed until a molding consistency was obtained.

The formulation of this example was evaluated for resistance to chemicalattack. In the test, the formulation was molded into the shape of areceptacle, fired to 1500° F., cooled and re-fired to 1500° F. Molten7075 aluminum alloy was poured into the receptacle and kept there for 72hours at 1500° F. Thereafter, a portion of the molten alloy waswithdrawn for chemical analysis. The chemical analysis of the portionwas compared to the chemical analysis of the starting alloy fordetermination of contamination. The analysis shows the silicon contentof the withdrawn alloy to be 0.8%, which is considered excellentresistance to molten aluminum for this classification of product. Thereceptacle from the subject invention exhibited no noticeablepenetration while a commercially available refractory, formed into areceptacle and treated in the same way, was totally penetrated by alloy.

The results of the analysis are provided in the following Table.

                  TABLE                                                           ______________________________________                                                               Standard                                                             Example 1                                                                              7075 Alloy                                             ______________________________________                                        Penetration     None                                                          into receptacle                                                               Reaction with   Slight -                                                      receptacle      some sticking                                                 surface         of alloy to                                                                   receptacle                                                    Analytical chemical                                                           analysis of                                                                   withdrawn alloy                                                               Si              0.80       0.10                                               Fe              0.20       0.20                                               Cu              1.70       1.60                                               Cr              0.22       0.22                                               Mg              2.50       2.50                                               Zn              5.75       5.75                                               Ti              0.03       0.03                                               ______________________________________                                    

Having thus described the invention, what is claimed is:
 1. A ceramicfiber containing refractory moldable composition suitable for use withmolten aluminum alloys, the composition comprised of:(a) 10-20 wt.%ceramic fiber; (b) 30.5-45 wt.% colloidal silica; (c) 30-45 wt.% totalcontent of liquid carrier; (d) 0.5-5 wt.% organic polymer; and (e) 1-25wt.% barium sulfate.
 2. The composition in accordance with claim 1wherein the ceramic fibers are in the range of 14 to 18 wt.%.
 3. Thecomposition in accordance with claim 1 wherein the colloidal silica isin the range of 35 to 42 wt.%.
 4. The composition in accordance withclaim 1 wherein the liquid carrier is in the range of 34 to 42 wt.%. 5.The composition in accordance with claim 1 wherein the barium sulfate isin the range of 2 to 10 wt.%.
 6. The composition in accordance withclaim 1 wherein the barium sulfate is in the range of 2 to 6 wt.%. 7.The composition in accordance with claim 1 wherein the ceramic fibersare selected from alumina, aluminum silicate, mullite, calcium aluminumsilicate, mineral wool and silicon carbide and mixtures thereof.
 8. Thecomposition in accordance with claim 1 wherein the fiber is aluminumsilicate.
 9. The composition in accordance with claim 1 wherein thecolloidal silica has a solids content in the range of 15-50 wt.% and aparticle size in the range of about 5-60 μm.
 10. The composition inaccordance with claim 1 wherein the liquid carrier is selected from thegroup consisting of water, methanol, ethanol, ethylene glycol anddiethylene glycol and mixtures thereof.
 11. The composition inaccordance with claim 1 wherein the carrier is water.
 12. Thecomposition in accordance with claim 1 wherein the polymer is a highmolecular weight, anionic, liquid acrylamide/acrylate polymer.
 13. Thecomposition in accordance with claim 11 wherein the ceramic fibers areselected from alumina, aluminum silicate, mullite, calcium aluminumsilicate, mineral wool and silicon carbide and mixtures thereof.
 14. Thecomposition in accordance with claim 11 wherein the ceramic fibers arealumina fibers.
 15. The composition in accordance with claim 11 whereinthe ceramic fibers are aluminum silicate fibers.
 16. The composition inaccordance with claim 11 wherein the ceramic fibers are mullite fibers.17. The composition in accordance with claim 11 wherein the ceramicfibers are mineral wool.
 18. The composition in accordance with claim 11wherein the ceramic fibers are silicon carbide.
 19. The composition inaccordance with claim 11 wherein the ceramic fibers are calcium aluminumsilicate.
 20. A ceramic fiber containing refractory moldable compositionsuitable for use with molten aluminum alloys, the composition comprisedof:(a) 10-20 wt.% ceramic fiber; (b) 5-17 wt.% colloidal alumina; (c)60-80 wt.% total content of liquid carrier; (d) 0.5-5 wt.% organicpolymer; and (e) 1-25 wt.% barium sulfate.